(133) Uterine Fluid Retention as a Mechanism for RU486 as a Contraceptive

Skyler Owens¹; Xiaoqin Ye^2,3

¹Integrative Physiology and Pharmacology Program, University of Georgia, Athens, GA, USA

²Interdisciplinary Toxicology Program, University of Georgia, Athens, GA, USA

³Department of Physiology and Pharmacology, College of Veterinary Medicine, University of Georgia, Athens, GA, USA

Abstract Text:

The fluid volume in the uterine cavity is dynamic prior to embryo implantation. At its peak volume upon ovulation, uterine fluid assists sperm migration to the oviduct/Fallopian tube for fertilization; and at its lowest volume upon the establishment of uterine receptivity, it facilitates embryo attachment to the uterine luminal epithelium (LE) for implantation. In ovariectomized rodents, estrogen and progesterone promote uterine fluid accumulation and reduction, respectively. Timely and coordinated hormonal levels are critical for early pregnancy events leading to embryo implantation. Therefore, hormonal contraceptives have been employed as a main approach for female contraception. RU486 / Mifepristone is a mixed progesterone receptor (PR) antagonist/agonist, and has been used in numerous clinical applications, including in termination of early pregnancy and as an emergency contraceptive. Upon administration, RU486, inhibits progesterone’s effects preventing the endometrium from thickening and loses receptivity to the embryo preventing implantation. RU486 in conjugation with misoprostol induces cervical softening and uterine contractility, facilitating the excretion to the embryo in abortion. One RU486 pill contains 200 mg (equivalent to 4~2 mg/kg for a woman in a body weight range of 50~100 kg); up to 800 mg RU486 was used in clinical studies; and up to 1800 mg RU486 was used in a tolerance test. Our dose-response and time-course study in mice, which have embryo attachment ~day 4.0 post-coitum (D4.0), revealed inhibition of embryo implantation by a single dose of RU486 (2-8 mg/kg) given between D2 @ 9 h and D3 @ 18 h, and the inhibitive effect of embryo implantation was correlated with excessive uterine fluid retention, prominently in the 4-8 mg/kg RU486 groups. Uterine fluid has not been systemically studied in infertile women. In women underwent in vitro fertilization-embryo transfer (IVF-ET), delayed uterine fluid absorption or uterine fluid retention were correlated with impaired or failed embryo implantation, respectively. Interestingly, fluid retention is a “side effect” of hormonal contraceptives. We propose that uterine fluid retention is a mechanism for RU486 as a contraceptive. To investigate the molecular mechanisms involving RU486-induced uterine fluid retention, we will employ our epiPR^-/- (Pgr^f/-Wnt7a^Cre/+) mouse model to determine the role of uterine epithelial PR in mediating RU486-induced uterine fluid accumulation; and to determine the spatiotemporal expression of selected channels with known functions in fluid movement, e.g., epithelial Na⁺ channel (ENaC), and aquaporins, in the uterus upon RU486 treatment. Our research will add uterine fluid dysregulation as a mechanism for hormonal contraceptives and will provide molecular insights into channels in temporal uterine fluid dynamics during early pregnancy for contraception and for treating infertility related to uterine fluid dysregulation.